1. Field of the Invention
The present invention relates to a transparent conductive layered structure having a transparent substrate and a transparent 2-layer film consisting of a transparent conductive layer and a transparent coating layer formed in succession on this substrate, which is used, for instance, as the front panel for displays, such as Braun tubes (CRTs), etc., and in particular, relates to a transparent conductive layered structure wherein the visible light transmittance of the transparent 2-layer film has been adjusted to a prescribed range less than 100%, a display in which this transparent conductive layered structure is used, and a coating liquid for forming a transparent conductive layer that is used in the production of transparent conductive layered structures.
2. Description of the Related Art
As a result of office automation in recent years, many OA machines have been introduced to offices and an environment where work must be done all day long facing a display of an OA machine is not uncommon today.
Taking a cathode ray tube (also referred to as the above-mentioned Braun tube; CRT) of a computer as an example of an OA machine, it has been required for the use of such CRTs that, in addition to being able to easily see the display screen in order to prevent a feeling of visual fatigue, adhesion of dust and electric shock attributed to electrification of the CRT screen, etc can be avoided. Furthermore, there recently has been concerned of the detrimental effects on the human body from the low-frequency magnetic waves generated from CRTs and it is desirable that the CRT not leak such electromagnetic waves to the outside.
In addition, the above-mentioned electromagnetic waves are generated from a deflecting coil or a flyback transformer and there is a tendency toward leakage of increasingly large amounts of electromagnetic waves to the surroundings with the development of larger televisions.
Leakage of a magnetic field can be prevented for the most part by precautions such as changing the shape of the deflection coil, etc. On the other hand, it is also possible to prevent leakage of an electric field by forming a transparent conductive layer on the front glass surface of the CRT.
Such methods of preventing leakage of electric field are theoretically the same as measures recently taken to prevent electrification. However, the above-mentioned transparent conductive layer must have a much higher conductivity than conductive layers that have been formed for preventing electrification. That is, although surface resistance of 108 xcexa9/xe2x96xa1 (ohm per square) is sufficient for preventing electrification, it is necessary to form a transparent conductive layer with a low resistance of at least 106 xcexa9/xe2x96xa1 or below, preferably 5xc3x97103 xcexa9/xe2x96xa1 or below, further preferably 103 xcexa9/xe2x96xa1 or below, to prevent leakage of an electric field (electric field shielding).
Thereupon, several proposals have been made in the past in response to the above-mentioned demands, and of these, the method whereby a coating liquid for forming a transparent conductive layer of conductive microparticles and inorganic binder, such as alkyl silicate, etc., dispersed in a solvent is applied and dried on the front glass of a CRT and then baked at a temperature of about 200xc2x0 C. is known as a method by which low surface resistance can be realized at a low cost.
Moreover, this method that uses a coating liquid for forming a transparent conductive layer is much more simple compared to other methods of forming transparent conductive layers, such as vacuum evaporation and sputtering, production cost is also low, and it is very useful for electric field shielding by which CRTs can be treated.
A coating liquid that uses indium tin oxide (ITO) for conductive microparticles is known as the coating liquid for the above-mentioned transparent conductive layer used in this method. However, since surface resistance of the film that is obtained is high at 104 to 106 xcexa9/xe2x96xa1, a corrective circuit for canceling the electric field is necessary in order to adequately block electric field leakage and therefore, there was a problem in that production cost rises accordingly. On the other hand, transmittance of film from a coating liquid for forming a transparent conductive layer using metal powder as the above-mentioned conductive microparticles is somewhat lower than that from coating liquid that uses ITO, but a film with low resistance of 102 to 103 xcexa9/xe2x96xa1 is obtained. Consequently, there is an advantage in terms of cost because the above-mentioned corrective circuit is not necessary and this will probably become mainstream in the future.
Moreover, the metal microparticles that are used for the above-mentioned coating liquid for forming a transparent conductive layer are limited to noble metals, such as silver, gold, platinum, rhodium, palladium, etc., which rarely oxidize in air, as shown in Japanese Laid-Open Patent Application No. Hei 8-77832 and Japanese Laid-Open Patent Application No. Hei 9-55175. This is because when metal microparticles other than a noble metal, such as iron, nickel, cobalt, etc., are used, an oxide film always forms on the surface of these metal microparticles in an air ambient atmosphere and good conductivity as a transparent conductive layer is not obtained.
On the other hand, anti-glare treatment is performed on the face panel surface in order to control reflection on the screen and thereby make the display screen easy to see. This anti-glare treatment is done by the method whereby diffused reflection at the surface is increased by making fine irregularities in the surface. However, this method cannot be said to be very desirable because image quality drops due to a reduction in resolution when it is used. Consequently, it is preferred that, instead, anti-glare treatment by the interference method be performed whereby the index of refraction of the transparent film and film thickness are controlled so that there is destructive interference of reflected light on incident light. In order to obtain low-reflection results by this type of interference method, a 2-layered film is generally used wherein optical film thickness of a film with a high index of refraction and a film with a low index of refraction is set at 1/4xcex and 1/4xcex (xcex is wavelength), respectively, or 1/2xcex and 1/4xcex, respectively. Film consisting of the above-mentioned indium tin oxide (ITO) microparticles is also used as this type of film with a high index of refraction.
Furthermore, of the optical constant of metals (nxe2x88x92ik, n: index of refraction, i2=xe2x88x921, k: extinction coefficient), the value of n is small, but the value of k is very high when compared to ITO, etc., and therefore, even if a transparent conductive layer consisting of metal microparticles is used, the same anti-reflection results as with ITO are obtained by interference with light by film with a 2-layer structure.
The metal microparticles that are used in conventional coating liquids for forming transparent conductive layers are limited to noble metals, such as silver, gold, platinum, rhodium, palladium, etc., as previously mentioned, but when their electrical resistance is compared, specific resistance of platinum, rhodium, and palladium is 10.6, 5.1, and 10.8 xcexcxcexa9xc2x7cm, respectively, which is high in comparison to the 1.62 and 2.2 xcexcxcexa9xc2x7cm of silver and gold. Therefore, there was an advantage to using silver microparticles and gold microparticles for forming a transparent conductive layer with low surface resistance.
Nevertheless, when silver microparticles were used, there were problems with weather resistance in that there was extreme sulfidation and oxidation and degradation by brine, ultraviolet rays, etc., while when gold microparticles were used, there were none of the above-mentioned problems with weather resistance, but there were the same problems with cost as when platinum microparticles, rhodium microparticles, palladium microparticles, etc., were used.
In light of this technical background, the inventor previously proposed a coating liquid for forming a transparent conductive layer in which noble metal-coated silver microparticles with a mean particle diameter of 1 to 100 nm, wherein of gold or platinum only, or a compound of gold and platinum, is coated on the surface of silver microparticles, are dispersed in place of the above-mentioned silver or gold microparticles, as well as a transparent conductive layered structure that is produced using this coating liquid and a display that uses this layered structure, etc. (refer to Japanese Laid-Open Patent No. Hei 11-203943, Japanese Laid-Open Patent Application No. Hei 11-228872, and Specification of Japanese Patent Application No. Hei 11-366343).
Moreover, when the surface of silver microparticles is coated with gold or platinum only or a compound of gold and platinum, the silver within the noble metal-coated silver microparticles is protected by the gold or platinum only or the compound of gold and platinum and therefore, improvement of weather resistance, chemical resistance, etc., is expected.
Furthermore, the phenomenon is confirmed whereby, during the course of production of transparent conductive layered structures, depending on the heat treatment conditions used for the above-mentioned noble metal-coated silver microparticles with a mean particle diameter of 1 to 100 nm, wherein gold or platinum only or a compound of gold and platinum is coated on the surface of silver microparticles, part of the silver diffuses to inside the coating layer formed from the gold and/or platinum to form an alloy layer and some of this alloy layer is exposed at the surface, resulting in a slight reduction in weather resistance, chemical resistance, etc.
It is also confirmed that this can be avoided by setting the gold and/or platinum content in the above-mentioned noble metal-coated silver microparticles in the range of 50 to 95 wt %.
Furthermore, it is possible to form the alloy layer obtained by the above-mentioned heat treatment on microparticles in a transparent conductive layer composed of silver and gold, etc., and there are cases where the noble-metal coating layer that coats the silver microparticle surface is not composed of only gold and/or platinum as a result of this alloy layer formation. Therefore, in the present specification the above-mentioned microparticles composed of silver and gold, etc., in the transparent conductive layer hereafter are not represented as noble metal-coated silver microparticles, but rather noble metal microparticles.
In addition to the above-mentioned demands for properties of good conductivity, low reflectance, weather resistance, chemical resistance, etc., recently there has also come to be a demand for improved contrast of an image by adjusting transmittance of this type of transparent conductive layered structure to within a prescribed range less than 100% (40 to 75%) in order to make the display screen even easier to see.
Consequently, there is a problem with the conventional transparent conductive layered structures in Japanese Laid-Open Patent Application Nos. Hei 11-203943, Hei 11-228872, and Japanese Patent Application No. Hei 11-366343 in that they cannot meet the above-mentioned demand.
The method disclosed in the above-mentioned specifications whereby a conventional transparent 2-layer film is formed on the surface of a face panel (CRT front panel) with a low transmittance (for instance, 40%xcx9c60%) and the method whereby a transparent 2-layer film with a low transmittance is formed on the surface of a face panel with high transmittance can be considered in response to these demands, while the latter method is favorable in terms of the fact that the transmittance of the CRT can be controlled as needed. Furthermore, progress has recently been made in flattening the display surface of CRT displays and the later method, the purpose of which is to make transmittance of a front panel uniform, is necessary in this case as well.
Therefore, an object of the present invention is to provide a first or second transparent conductive layered structure wherein the transparent conductive layer or the transparent coating layer comprising the above-mentioned transparent 2-layer film has a low transmittance, there is the same good conductivity, low reflectance, and weather resistance, chemical resistance, etc., as in the past, and the visible light transmittance of the transparent 2-layer film is adjusted to within a prescribed range less than 100% (40 to 75%).
Another object of the present invention is to provide a display with which contrast of the display screen is improved and surface reflection of the display screen is reduced, and which has long-term strong electric field shielding effects.
Yet another object of the present invention is to provide a coating liquid for forming a transparent conductive layer that is suitable for the manufacture of the above-mentioned first transparent conductive layered structure.
That is, the first transparent conductive layered structure according to the present invention is a transparent conductive layered structure having a transparent substrate and a transparent 2-layer film consisting of a transparent conductive layer and a transparent coating layer formed in succession on this transparent substrate, wherein the main components of the above-mentioned transparent conductive layer are noble metal microparticles with a mean particle diameter of 1 to 100 nm composed of gold and/or platinum and silver and containing 5 to 95 wt % of the above-mentioned gold and/or platinum, colored pigment microparticles with a mean particle diameter of 5 to 200 nm, and binder matrix, and the above-mentioned noble metal microparticles are mixed at a ratio of 1 to 40 parts by weight per 1 part by weight colored pigment microparticles, the above-mentioned transparent 2-layer film having a surface resistance of 10 to 5,0000 Zxcexa9/xe2x96xa1, a reflectance of the transparent 2-layer film which becomes minimum in the reflection profile of the visible light region being 0 to 2.5%, visible light transmittance of the transparent 2-layer film only not including the above-mentioned transparent substrate being 40 to 75%, and standard deviation of transmittance of only the transparent 2-layer film not including the above-mentioned transparent substrate being 0 t0 5% at each wavelength in 5 nm intervals in the visible light wavelength region (380 to 780 nm).
Moreover, the second transparent conductive layered structure according to the present invention is a transparent conductive layered structure having a transparent substrate and a transparent 2-layer film comprising a transparent conductive layer and transparent coating layer formed in succession on this transparent substrate,
wherein the main components of the above-mentioned transparent conductive layer are noble metal microparticles with a mean particle diameter of 1 to 100 nm composed of gold and/or platinum and silver and containing 5 to 95% gold and/or platinum and binder matrix, and the main components of the above-mentioned transparent coating layer are colored pigment microparticles with a mean particle diameter of 5 to 200 nm and binder matrix, the above-mentioned transparent 2-layer film has a surface resistance of 10 to 5,000 xcexa9/xe2x96xa1, reflectance of the above-mentioned 2-layer film which becomes minimum in the reflection profile of the visible light region being 0 to 2.5%, visible light transmittance of the transparent 2-layer film only not including the above-mentioned transparent substrate being 40 to 75%, and standard deviation in transmittance of the transparent 2-layer film only not including the above-mentioned transparent substrate being 0 to 5% at each wavelength in 5 nm intervals of the visible light wavelength region (380 to 780 nm).
Next, the display according to the present invention is characterized in that it is a display comprising a display main unit and a front panel arranged on the front side of this display main unit,
wherein the above-mentioned first or second transparent conductive layered structure is used as the above-mentioned front panel with the transparent 2-layer film side disposed on the outside.
Moreover, the coating liquid for forming a transparent conductive layer according to the present invention used in the production of the above-mentioned first transparent conductive layered structure is a coating liquid for forming a transparent conductive layer of a transparent conductive layered structure having a transparent substrate and a transparent 2-layer film consisting of a transparent conductive layer and a transparent coating layer formed in succession on this transparent substrate, the above-mentioned transparent 2-layer film having a surface resistance of 10 to 5,000 xcexa9/xe2x96xa1, reflectance of the above-mentioned 2-layer film which becomes minimum in the reflection profile of the visible light region being 0 to 2.5%, and the visible light transmittance of the transparent 2-layer film only not including the above-mentioned transparent substrate being 40 to 75%, while standard deviation of transmittance of the transparent 2-layer film only not including the above-mentioned transparent substrate being 0 to 5% at each wavelength in 5 nm intervals of the visible light wavelength region (380 to 780 nm), wherein the main components of said coating liquid are noble metal-coated silver microparticles with a mean particle diameter of 1 to 100 nm containing 5 to 95 wt % gold and/or platinum, and the surface of which is coated with gold or platinum alone or a compound of gold and platinum, colored pigment microparticles with a mean particle diameter of 5 to 200 nm, and a solvent in which these microparticles are dispersed, and the noble-metal coated silver microparticles are mixed at a ratio of 1 to 40 parts by weight per 1 part by weight of the above-mentioned colored pigment microparticles.